Im trying to validate Digital Signature manually. However, my status of my signature always appear to be IdentityUnverifiable. Can anyone tell me what are the necessary steps needed to change my status of my signature to be valid?

I have added the public key in the Trusted Identites section in the Adobe Reader. However, it did not appear in Contacts page but appear in the Certificate page. Is there something wrong?

Another problem is that i have only Adobe Reader installed but not Adobe Acrobat. Is that the reason why I can't certify my document? Does this lead to why the status of the signature always appear to be IdentityUnverifiable? Your help will be greatily appreciated.

Reader is all that is needed to validate signatures. It sounds like you have not established a trust relationship with the signer successfully. In Reader, go to Document > Manage Trusted Identities and then select the Certificates display. Is the signer or the issuer of the signer's certificate listed there? If not, you need to add it. If so, click on it a select Edit Trust... The "Use this certificate as a trusted root" box needs to be checked (Acrobat/Reader 9) or "Signatures and as a trusted root" (Acrobat/Reader 8).

If the desired certificate isn't listed, the easiest way to add it is, from the signature, right click show signature properties, Click Show Certificate. From there, select the cert (or its parent or issuer), then click the Trust tab, then click Add To Trusted Identities. Be sure the trusted root checkbox is set before clicking ok a bunch of times.